add extraFiles to mkNteDerivation

not so simple anymore is it

nte-drv.nix

@@ -5,7 +5,12 @@ pkgs: engine: {
   extraArgs ? {},
   entries ? [],
   templates ? [],
-}: pkgs.stdenv.mkDerivation {
+  extraFiles ? []
+}: let
+  inherit (pkgs) lib;
+  inherit (lib.lists) forEach init;
+  inherit (lib.strings) concatStrings match normalizePath optionalString splitString;
+in pkgs.stdenv.mkDerivation {
   inherit name version src;
 
   buildPhase = /*sh*/''
@@ -15,4 +20,23 @@ pkgs: engine: {
 
     runHook postBuild
   '';
+
+  installPhase = optionalString (extraFiles != []) /*sh*/''
+    runHook preInstall
+
+    mkdir -p $out
+
+    ${concatStrings (forEach extraFiles
+        (extraFile: let
+          isInSubdir = (match ".+/.+" extraFile.destination) != null;
+          outDir = concatStrings (init (splitString "/" extraFile.destination));
+          outPath = normalizePath "$out/${extraFile.destination}";
+        in /*sh*/''
+          ${optionalString isInSubdir /*sh*/"mkdir -p ${outDir}"}
+          cp -r ${extraFile.source} ${outPath}
+        ''))
+    }
+
+    runHook postInstall
+  '';
 }